Packages with molding material forming steps

ABSTRACT

A package includes a first package component having a top surface, a second package component bonded to the top surface of the first package component, and a plurality of electrical connectors at the top surface of the first package component. A molding material is over the first package component and molding the second package component therein. The molding material includes a first portion overlapping the second package component, wherein the first portion includes a first top surface, and a second portion encircling the first portion and molding bottom portions of the plurality of electrical connectors therein. The second portion has a second top surface lower than the first top surface.

This application claims the benefit of U.S. Provisional Application No.61/782,064, filed Mar. 14, 2013, and entitled “Packages with MoldingMaterial Forming Steps,” which application is hereby incorporated hereinby reference.

BACKGROUND

In a conventional package-on-package (POP) process, a top package, inwhich a first device die is bonded, is further bonded to a bottompackage through solder balls. The bottom package may also include asecond device die bonded therein. The second device die may be on thesame side of the bottom package as the solder balls.

Before the bonding of the top package to the bottom package, a moldingcompound is applied on the bottom package, with the molding compoundcovering the second device die and the solder balls. Since the solderballs are buried in the molding compound, a laser ablation or drillingis performed to form holes in the molding compound, so that the solderballs are exposed. The top package and the bottom package may then bebonded through the solder balls in the bottom package. In addition, themolding compound may be filled into the space between the second devicedie and a package substrate in the bottom package. Since the spacebetween the second device die and the package substrate in the bottompackage is small, a void may be adversely generated in the space, whichresults in stress to the second device die.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIGS. 1A through 8 are cross-sectional views and top views ofintermediate stages in the manufacturing of a package-on-packagestructure in accordance with some exemplary embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable concepts that can be embodied in a wide varietyof specific contexts. The specific embodiments discussed areillustrative, and do not limit the scope of the disclosure.

A package and the method of forming the same are provided in accordancewith various embodiments. The intermediate stages of forming thepackages are illustrated in accordance with some embodiments. Thevariations of the embodiments are discussed. Throughout the variousviews and illustrative embodiments, like reference numbers are used todesignate like elements.

Referring to FIG. 1A, package substrates 10 are provided. Packagesubstrates 10 may be parts of package substrate strip 100. For example,FIG. 1B illustrates a top view of exemplary package substrate strip 100,which includes a plurality of package substrates 10 arranged as anarray. Throughout the description, although reference numeral 10 refersto package substrates, it may also be used to refer to other types ofpackage components such as interposers. Throughout the description,package substrates 10 are alternatively referred to as first packagecomponents.

Referring back to FIG. 1A, package substrates 10 may include substrates18 that are formed of a dielectric material. Alternatively, substrates18 may be formed of a semiconductor material such as silicon. In someembodiments, substrates 18 are laminate substrates, which include aplurality of dielectric films adhered together through lamination. Inalternative embodiments, substrates 18 are build-up substrates. Whensubstrates 18 are formed of dielectric materials, the dielectricmaterials may comprise composite materials that are mixed with glassfiber and/or resin. Package substrates 10 are configured to electricallycouple electrical connectors 12 on first surface 10A to conductivefeatures 16 on second surface 10B, wherein surfaces 10A and 10B areopposite surfaces of package substrates 10. Conductive features 16 maybe metal pads, for example. Package substrates 10 further includeconductive connections such as metal lines/vias 14 therein.Alternatively, features 14 comprise through-vias penetrating throughsubstrates 18.

Device dies 20 are bonded to package substrates 10 through electricalconnectors 12. Dies 20 may be circuit dies comprising integrated circuitdevices (not shown) such as transistors, capacitors, inductors,resistors, and the like. Dies 20 may also be logic dies such as CentralComputing Unit (CPU) dies. The bonding of dies 20 to electricalconnectors 12 may be through solder bonding or direct metal-to-metalbonding (such as copper-to-copper bonding). Throughout the description,device dies 20 are alternatively referred to as second packagecomponents.

Electrical connectors 24 are formed on top surfaces 10A of packagesubstrates 10. Electrical connectors 24 are electrically coupled to, andmay be in physical contact with, electrical connectors 12 and conductivefeatures 16. In some embodiments, electrical connectors 24 are solderballs. In alternative embodiments, electrical connectors 24 comprisemetal pads, metal pillars, solder caps formed on metal pillars, and/orthe like. The solder regions (such as solder balls or the reflowedsolder caps) of electrical connectors 24 may have round top surfaces,although the top surfaces of the solder regions may also be planar.Electrical connectors 24 are not covered by dies 20. In someembodiments, top ends 24A of electrical connectors 24 are higher thantop surfaces 20A of dies 20. In alternative embodiments, top ends 24A ofelectrical connectors 24 are substantially level with, or lower than,top surfaces 20A of dies 20.

Referring to FIG. 2, mold chase 26 is provided. Mold chase 26 may beformed of stainless steel, aluminum, copper, ceramic, or othermaterials. Recesses 28 are formed in mold chase 26. Recesses 28 may forman array in a top view of mold chase 26, wherein the locations and thesizes of recesses 28 correspond to the locations and the sizes of dies20 (FIG. 1B). In some embodiments, depth D1 of recesses 28 are greaterthan about 30 μm or greater than about 50 μm. It is appreciated,however, that the values recited throughout the description are merelyexamples, and may be changed to different values. Mold chase 26 thusincludes surfaces 26A outside of recesses 28, and surfaces 26B insiderecesses 28. In some embodiments, as shown in FIG. 2, surfaces 26A and26B are substantially planar surfaces. In alternative embodiments,surfaces 26A and 26B may have other shapes. For example, surfaces 26Bmay be curved, as indicated by dashed lines. Recesses 28 also havesidewalls 27. In some embodiments, sidewalls 27 are straight verticalsidewalls perpendicular to surfaces 26A and/or 26B. In alternativeembodiments, sidewalls 27 are slanted, as shown by dashed line. In yetalternative embodiments, sidewalls 27 may also be curved, as alsoillustrated using dashed lines.

Referring to FIG. 3, a blanket release film 30 is adhered to mold chase26. The resulting release film 30 includes portions outside of recesses28, and portions extending into recesses 28. Release film 30 is formedof a relatively soft material, so that when solder balls are pressedinto it, the solder balls are not damaged, and the solder balls maysubstantially maintain their shapes. For example, release film 30 may bea fluorine-base film, a silicon-coated polyethylene terephthalate film,a polymethylpentene film, a polypropylene film, or the like. Mold chase26 may comprise small through-holes (not shown) extending from topsurface 26C to surfaces 26A and 26B, so that air may be evacuated fromthe through-holes, and release film 30 may have good contact with thesidewalls of mold chase 26 (which sidewalls are in recesses 28) and thebottom surfaces 26A and 26B of mold chase 26. Accordingly, substantiallyno air bubble is formed between release film 30 and mold chase 26.Release film 30 also forms cavities following the profile of recesses28, which cavities are also shown as recesses 28.

Referring to FIG. 4, mold chase 26 and release film 30 are placed overpackage substrate strip 100. The centers of dies 20 may be aligned tothe centers of recesses 28 in mold chase 26. In some embodiments, topsurfaces 20A of dies 20 are higher than surfaces 26A of mold chase 26,and hence dies 20 partially extend into recesses 28. In alternativeembodiments, top surface 20A of dies 20 are lower than surfaces 26A ofmold chase 26, and hence dies 20 are outside of recesses 28. Mold chase26 and release film 30 are pressed against package substrate strip 100,wherein arrows 29 represent the pressing force. The top portions ofelectrical connectors 24 are hence pressed into release film 30. Thebottom portion of each of electrical connectors 24 remains outside ofrelease film 30.

Referring to FIGS. 5A and 5B, molding material 32, which is in a liquidform, is injected into the space between release film 30 and packagesubstrate strip 100. Molding material 32 may be a Molding Underfill(MUF) in some embodiments, although other types of polymers/resins mayalso be used. Molding material 32 fills the gaps between dies 20 andrelease film 30 and the spaces between dies 20 and package substratestrip 100. Also, molding material 32 encircles, and is in contact with,electrical connectors 24. As shown in FIG. 5B, which is a top view ofthe structure in FIG. 5A, molding material 32 is injected from one sideof package substrate strip 100, and flows to the other side. Eventually,molding material 32 fills the entire space between release film 30/moldchase 26 and package substrate strip 100. After the injection of moldingmaterial 32, molding material 32 is cured and solidified.

Referring to FIG. 6, mold chase 26 and release film 30 are removed. Thestructure shown in FIG. 6 is then sawed apart into a plurality ofpackages 200, as shown in FIG. 7. Each of packages 200 includes one ofpackage substrates 10, one of dies 20, and the respective overlyingportion of molding material 32. Throughout the description, packages 200are referred to as bottom packages.

FIGS. 7A and 7B illustrate a cross-sectional view and a top view,respectively, of bottom package 200. As shown in FIG. 7A, in theresulting bottom package 200, molding material 32 comprises firstportions 32′ overlapping dies 20. Thickness T1 of the first portion 30′may be greater than about 30 μm, although thickness T1 may also besmaller than about 30 μm. Thickness T1 is also selected so that in thesubsequent packaging step as shown in FIG. 8, the molding materialportion 32′ does not prevent electrical connectors 24 from being joinedto the respective top package 300. As shown in FIG. 7A, die 20 is moldedusing an over-mold scheme. On the other hand, electrical connectors 24have their top portions exposed out of molding material 32. Hence,electrical connectors 24 are molded using an exposed-mold scheme.Molding material 32 includes surfaces 32A and 32B, which areinterconnected by sidewalls 33 of molding material 32. Surfaces 32A and32B and sidewalls 33 thus form steps. Surfaces 32A and 32B may comprisesubstantially planar portions that are substantially parallel to eachother. Furthermore, since surfaces 32A and 32B are defined by the bottomsurfaces of the same release film 30 (FIG. 5A), surfaces 32A and 32Bwill have a same surface roughness. The height difference D2 betweensurfaces 32A and 32B, which height difference D2 is also the height ofsteps 34, may be greater than about 30 μm. Furthermore, in someembodiments, surface 32A has an area larger than the area of die 20, andmay laterally extend beyond the edges of the die 20 by distance D3,which is a non-zero value. In some exemplary embodiments, distance D3 isgreater than about 30 μm. Accordingly, steps 34 are located between theedges of dies 20 and the respective nearest electrical connectors 24.FIG. 7B illustrates a top view of the structure in FIG. 7A. In someembodiments, step 34 is substantially vertical. In alternativeembodiments, step 34 is slanted, with the lower portions of moldingmaterial portion 32′ wider than the respective upper portions. Slantangle α may be between 90 degrees and about 135 degrees, for example,although slant angle α may be greater. The corners of step 34 may berounded or form substantially straight angles.

As shown in FIG. 7B, step 34 may form a ring encircling die 20.Electrical connectors 24 are disposed outside the ring formed of steps34, and may also be aligned to a plurality of rings that encircles thering of steps 34.

In alternative embodiments in which electrical connectors 24 have flatsurfaces, in the molding of molding material 32 (the step shown in FIGS.5A and 5B), release film 30 may not be used. Instead, mold chase 26 maycontact the top surfaces of electrical connectors 24. In the resultingstructure in accordance with these embodiments, top surfaces 32B (FIG.7A) of molding material 32 will be level with the flat top surfaces ofelectrical connectors 24, wherein the flat top surfaces of electricalconnectors 24 are exposed through molding material 32.

FIG. 8 illustrates the bonding of top package 300 to bottom package 200.In the bonding process, top package 300 is first placed against bottompackage 200. Top package 300 may be a package that includes device dies302 and package substrate 304, wherein device dies 302 are bonded topackage substrate 304. In some exemplary embodiments, device dies 302comprise memory dies such as Static Random Access Memory (SRAM) dies,Dynamic Random Access Memory (DRAM) dies, or the like. Furthermore,before the bonding of top package 300 to bottom package 200, moldingmaterial 306 may be pre-molded on device dies 302 and package substrate304. In some embodiments, top package 300 includes solder regions (notshown) that are aligned to electrical connectors 24 (FIG. 7A). After areflow process, the solder regions in top package 300 are merged withthe solder in electrical connectors 24 to form solder regions 36, whichjoin top package 300 to bottom package 200.

In the embodiments of the present disclosure, the molding material ismolded using a hybrid scheme, wherein the dies in the bottom packagesare molded in the molding material. Hence, the dies are molded using anover-mold scheme. The electrical connectors of the bottom packages,however, are molded using an expose-mold scheme. Advantageously, withthe over-molding of the dies, more molding material may be disposed inthe bottom package. The molding material may contract (for example,during the curing process) after being molded, and hence has the effectof reducing the warpage of the bottom packages. As a result, using moremolding material in the bottom package may reduce the warpage more. Onthe other hand, by using exposed-mold for the electrical connectors inthe bottom packages, the sizes of the electrical connectors in thebottom packages may be reduced, and the pitches of the electricalconnectors in the bottom packages may be reduced. Furthermore, toachieve the exposed-mold, the height of the molding material surroundingthe electrical connectors is reduced. Accordingly, in the moldingprocess, the channels for molding material to flow around the electricalconnectors become smaller. This forces the molding material to flowthrough the spaces between the dies and the package substrates in thebottom packages, and hence the likelihood of forming voids in the spacesbetween the dies and the package substrates is reduced.

In accordance with some embodiments, a package includes a first packagecomponent having a top surface, a second package component bonded to thetop surface of the first package component, and a plurality ofelectrical connectors at the top surface of the first package component.A molding material is over the first package component and molding thesecond package component therein. The molding material includes a firstportion overlapping the second package component, wherein the firstportion includes a first top surface, and a second portion encirclingthe first portion and molding bottom portions of the plurality ofelectrical connectors therein. The second portion has a second topsurface lower than the first top surface.

In accordance with other embodiments, a package includes a packagesubstrate, which includes first metal pads at a top surface of thepackage substrate, second metal pads at a bottom surface of the packagesubstrate, and conductive connections interconnecting the first metalpads to the second metal pads. A die is over and bonded to the firstmetal pads. A plurality of electrical connectors is over and bonded tothe package substrate. A molding material is molded over the packagesubstrate. The molding material has a first top surface and a second topsurface encircling the first top surface in a top view of the package,wherein the second surface is lower than the first top surface.

In accordance with yet other embodiments, a method includes bonding aplurality of dies to a plurality of package substrates of a packagesubstrate strip, and placing a mold chase over the package substratestrip. The mold chase has a plurality of recesses, each aligned to oneof the plurality of dies. The mold chase further includes first bottomsurfaces in the plurality of recesses, and second bottom surfacesoutside of, and between, the plurality of recesses, wherein the secondbottom surfaces are lower than the first bottom surfaces. The methodfurther includes injecting a molding material into a space between themold chase and the package substrate strip, curing the molding material,and removing the mold chase.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A package comprising: a first package componentcomprising a top surface; a second package component bonded to the topsurface of the first package component; a plurality of electricalconnectors at the top surface of the first package component; and amolding material over the first package component and molding the secondpackage component therein, wherein the molding material comprises: afirst portion overlapping the second package component, wherein thefirst portion comprises a first top surface; and a second portionencircling the first portion and molding bottom portions of theplurality of electrical connectors therein, wherein the second portioncomprises a second top surface lower than the first top surface, withthe first top surface and the second top surface having a same surfaceroughness.
 2. The package of claim 1, wherein the molding materialfurther comprises a sidewall connecting the first top surface to thesecond top surface, wherein the first top surface, the sidewall, and thesecond top surface form a step.
 3. The package of claim 2, wherein thestep forms a ring encircling the second package component.
 4. Thepackage of claim 2, wherein the step has a height greater than about 30μm.
 5. The package of claim 2, wherein the sidewall is not perpendicularto the second top surface.
 6. The package of claim 1, wherein theplurality of electrical connectors further comprises top portions abovethe second top surface of the second portion of the molding material. 7.The package of claim 1, wherein the first portion has a top-view areagreater than a top view area of the second package component, andwherein edges of the first portion of the molding material extend beyondedges of the second package component.
 8. The package of claim 1,wherein the first portion of the molding material has a thicknessgreater than about 30 μm.
 9. A package comprising: a package substratecomprising: first metal pads at a top surface of the package substrate;second metal pads at a bottom surface of the package substrate; andconductive connections interconnecting the first metal pads to thesecond metal pads; a die over and bonded to the first metal pads; aplurality of electrical connectors over and bonded to the packagesubstrate, wherein each of the plurality of electrical connectorscomprises: a round top surface; and a round sidewall smoothly andcontinuously connected to the round top surface with no abrupt change; amolding material molded over the package substrate, wherein the moldingmaterial comprises: a first top surface; and a second top surfaceencircling the first top surface in a top view of the package, whereinthe second surface is lower than the first top surface and the round topsurface of the each of the plurality of electrical connectors, whereinthe first top surface and the second top surface of the molding materialhave a same surface roughness, and wherein the second surface has acorner in contact with the sidewall of one of the plurality ofelectrical connectors.
 10. The package of claim 9, wherein the first topsurface comprises a center portion overlapping the die.
 11. The packageof claim 10, wherein the first top surface further comprises an outerportion encircling the center portion of the first top surface, whereinthe outer portion is misaligned with the die.
 12. The package of claim9, wherein the second top surface encircles each of the plurality ofelectrical connectors.
 13. The package of claim 9, wherein the first topsurface and the second top surface form a step, and wherein the stepforms a ring encircling the die.
 14. The package of claim 13, whereinthe step has a height greater than about 30 μm.
 15. The package of claim9 further comprising a top package over the molding material, whereinthe top package is bonded to the package substrate through the pluralityof electrical connectors.
 16. The package of claim 9, wherein themolding material further comprises a sidewall connecting the first topsurface to the second top surface, with the sidewall not perpendicularto the second top surface.
 17. A package comprising: a package substratecomponent comprising a top surface; a device die component bonded to thetop surface of the package substrate; a plurality of electricalconnectors at the top surface of the package substrate; and a moldingmaterial over the package substrate and molding the device die therein,wherein the molding material comprises: a first portion overlapping thedevice die, wherein the first portion comprises a first top surface; asecond portion encircling the first portion and molding bottom portionsof the plurality of electrical connectors therein, wherein the secondportion comprises a second top surface lower than the first top surface,and the first top surface and the second top surface have a same surfaceroughness; and a sidewall connecting the first top surface to the secondtop surface, wherein the first top surface, the sidewall, and the secondtop surface form a step, and the sidewall is slanted.
 18. The package ofclaim 17, wherein the sidewall and the second surface form an anglebetween 90 degrees and about 135 degrees.
 19. The package of claim 17,wherein the step forms a ring encircling the device die.
 20. The packageof claim 17, wherein the step has a height greater than about 30 μm.